1. Field of the Invention
The present invention relates to a stream data distributing method and system, and more particularly to stream data distributing techniques capable of preventing illegal accesses to a stream data distributing server by a security mechanism such as a firewall.
2. Description of the Related Art
A stream data distributing system is generally constituted of a stream server and clients. The stream server has a storage for storing contents (e.g., image data and the like) and distributes stored contents. Each client transmits a stream data distribution request to the sever and reproduces the received stream data.
A firewall is software or hardware installed between the Internet and a network (LAN) used only in a private organization. The firewall prevents illegal accesses to LAN by monitoring network traffic at LAN and allowing only permitted packets to pass. The firewall permits only a packet whose protocol and destination port are allowed to be transmitted or received by using these protocol and port as permission keys. “Firewall Support”, [online], by RealNetworks (registered trademark of RealNetworks, Inc, Internet URL: http://service.real.com/firewall/adminrs.html) proposes two stream data distributing methods in order to prevent illegal accesses to a stream server. One method distributes stream data by a UDP/IP transport protocol which allocates a dynamic port, and the other method distributes stream data by an HTTP protocol which allocates a static port.
When a stream server distributes stream data to a client in the same LAN as that of the stream server on the same side of a firewall, the stream server can distribute the stream data by the “UDP/IP protocol” using a “dynamic port” being designated by the client.
“Firewall Support” proposes the following two configurations in order to distribute stream data to a client on the Internet.
With one configuration, stream data is distributed by the “HTTP protocol” allocating the “static port”. If stream data is to be distributed by the “UDP/IP protocol” allocating the “dynamic port”, it is necessary to set the firewall in such a manner that all packets having ports settable by clients are permitted to be passed. However, this setting poses some security problem. In view of this, in order to distribute stream data to a client on the Internet by preventing illegal accesses to LAN, the stream data distributing method with the “HTTP protocol” allocating the “static port” has been proposed, with which method only particular destination ports can be set to the firewall.
With the other configuration, a stream server is installed also on the Internet outside the firewall. Since the stream server is installed outside the firewall, stream data can be distributed by the “UDP/IP protocol” allocating the “dynamic port” while illegal accesses to LAN are prevented.